Polyester films typified by polyethylene terephthalate film are widely used in industrial fields because polyester films have excellent mechanical properties, heat resistance and chemical resistance. Among others, the demand for process materials has recently remarkably grown; in particular, mold release materials, belonging to one category of process materials, are widely used in electric and electronic fields. Examples of the application of the mold release material include protective materials for the pressure-sensitive adhesive/adhesive surface of pressure-sensitive adhesive materials such as pressure-sensitive adhesive sheets and pressure-sensitive adhesive tapes.
As a mold release material prepared by providing a resin layer having mold releasability on the surface of a polyester film, for example, Patent Literature 1 discloses a mold release sheet prepared by providing, with post-coating, a resin layer including a polypropylene-based modified polyolefin resin on a polyester film. However, when a pressure-sensitive adhesive material having a large peel strength is bonded to the resin layer provided through post-coating, the components of the resin layer sometimes migrate into the pressure-sensitive adhesive material, and hence the peeled-off pressure-sensitive adhesive material is degraded in pressure-sensitive re-adhesiveness, is low in residual adhesion rate and is disadvantageously impaired in the performances as a pressure-sensitive adhesive material.
Patent Literature 2 and Patent Literature 3 disclose mold release films being each prepared by providing, through inline coating, a resin layer including a polyethylene-based modified polyolefin resin on a polyester film. However, the resin layer including a polyethylene-based modified polyolefin resin is small in peel strength, and hence when the resin layer to which a pressure-sensitive adhesive material is bonded is subjected to punching processing, detachment sometimes occurs in the edge of the resin layer, and disadvantageously neat punching is sometimes impossible.
When a mold release film including a resin layer provided on one surface of a polyester film, described in each of Patent Literature 1 to Patent Literature 3, is wound in a form of a roll, the components of the resin layer sometimes migrate, depending on the composition of the resin layer, to the opposite surface to the surface provided with the resin layer to contaminate the opposite surface.